Due to the high temperatures of the flame prevailing in the kiln sulphur oxides and nitrogen oxides form in the kiln and have to be removed from the exhaust gases.
DE-A-100 11 327 describes a method for the simultaneous desulphurisation and denitrogenation without the formation of ammonium sulphate or ammonium hydrogen sulphate in which the breakdown of NOx to N2 and H2O takes place. The treatment of the exhaust gases containing sulphur oxides and nitrogen oxides is carried out in an apparatus which is equipped with a fixed catalytic converter and is disposed in the direction of flow of the exhaust gases to the heat exchanger.